Characterisation of sunflower root colonisation by Phoma macdonaldii

Abstract

Phoma macdonaldii, the causal agent of black stem disease of sunflower (Helianthus annuus), also attacks roots and collars of the plants, resulting in early death. Totally resistant lines do not exist for infection of the aerial parts, but tolerant lines have been characterised. This paper presents a study on colonisation of a partially resistant and a susceptible sunflower line by P. macdonaldii. The fungus was transformed with a constitutively expressed reporter gene encoding the jellyfish green fluorescent protein via Agrobacterium tumefaciens, and colonisation of sunflower roots by this transformed strain was studied by various microscopy techniques including confocal and scanning electron microscopy. The results show that penetration of the fungus into the root occurred through natural fissures or through the epidermis and was similar in both lines. In contrast, the colonisation rate of the stele was reduced in the partially resistant line, and the morphology of the fungal hyphae was also affected. The effect on hyphal morphology was strongest in the stele, indicating a localised production of defence compounds in this line.

Nitrogen and water management can limit premature ripening of sunflower induced by Phoma macdonaldii

“…However, under water stress, vascular wilt pathogens are involved in xylem vessel blockage (Beckman, 1964;Robb et al, 1981) leading to the death of the plant. P. macdonaldii hyphae were observed in the xylem of 10 day old seedlings (Abou Al Fadil et al, 2009) and of PR plants of cv. Heliasol RM (data not shown).…”

“…In addition, N supply should be adapted to cultivar susceptibility: the N optimum for a susceptible cultivar should be lower than for a partially resistant one. Since genotypes with partial resistance to P. macdonaldii have been described (Abou Al Fadil et al, 2009), the choice of the cultivar should be taken into account to limit PR in the future. In this study, the susceptibility to the disease was tested only on two cultivars, but significant differences were confirmed between them.…”

Different genetic architectures underlie crop responses to the same pathogen: the {Helianthus annuus * Phoma macdonaldii} interaction case for black stem disease and premature ripening

“…Several studies dealing with the genetic control of sunflower resistance to Phoma attacks on petiole stem base and roots of seedlings in growth chamber have demonstrated the quantitative character of this resistance [ 6 – 11 ]. Cytological observations of a susceptible and of a more resistant inbred line showed that the development of fungal hyphae within the stele was affected in the more resistant genotype, suggesting the involvement of a plant compound in the defense [ 12 ]. In addition, candidate genes could be identified through transcriptomic studies of the sunflower * P. macdonaldii interaction (e.g.…”

Phoma du tournesol et dessèchement précoce : point sur les avancées de la recherche

“…Ces résultats ont fait émerger la question de l'origine pathologique principale du dessèchement précoce et du rôle de ces champignons autres que le phoma. De nombreux travaux de recherche ont été menés en France depuis le début des années 1990, principalement sur l'épidémiologie du phoma (Delos et al, 1997 ;Delos et al, 1998) et sa variabilité (Larfeil, 2003), les méthodes de reproduction des symptômes sur plantules et sur plantes adultes (Larfeil et al, 2010), la progression du champignon à l'intérieur des tissus de la plante hôte (Roustaee et al, 2000 ;Abou al Fadil et al, 2009), le déterminisme génétique de la résistance du tournesol aux attaques de phoma sur différents organes (cotylédons, tige, collet, racines), sur plantules (Alignan, 2006 ;Roustaee et al, 2000 ;Bert et al, 2004 ;Abou Al Fadil, 2006 ;Abou Al Fadil et al, 2007a, b ;, l'impact de la conduite de culture sur l'incidence et la gravité des attaques sur tige (Debaeke et Pérès, 2003). Le dessèchement précoce fait partie des thèmes de recherche identifiés comme prioritaires pour le tournesol dans le programme de recherches « Tournesol 2010 ».…”